Re: [Xenomai] Floating point operations in kernel on powerpc

[Norbert Bukuli <norbert.bukuli@mediso.hu>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Dear Mr Gerum,

let me respond your letter below.

On 2013-02-13 18:15, Philippe Gerum wrote:
> On 02/13/2013 04:49 PM, Norbert Bukuli wrote:
>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
>> 
>> Dear Mr Gerum,
>> 
>> thank you for your kind answer. As you can see in the example
>> code I do not call explicitly either _savefpr_XX or
>> rthal_save_fpu and their restore counterparts. I only do some
>> floating point operations in a Xenomai domain kernel thread. 
>> However the linker misses the routines mentioned earlier. Are
>> there linker flags to change this behaviour? One important note,
>> in the kernel configuration the hardware FPU support is switched
>> on. (CONFIG_XENO_HW_FPU=y)
> 
> -msoft-float with hw FPU looks suspicious.
- -msoft-float is defined by the kernel's make system, but if you read
the line further you can see, that I set the -mhard-float compiler flag.

I don't understand why you
> mention C runtime libraries when building kernel modules either.
It is probably my bad english, sorry for that.
I mentioned the c runtime library, because there is a file a kernel
source: arch/powerpc/lib/crtsavres.S
One can see in this file: "Based on gcc/config/rs6000/crtsavres.asm
from gcc".

> Building with eldk 5.2.1 for fpu-enabled 6xx cores can be done
> with 
> eldk-5.2.1/powerpc/sysroots/i686-eldk-linux/usr/bin/powerpc-linux/powerpc-linux-gcc
>
> 
from a stock eldk install.
I use eldk-switch for set the environmental variables corresponding to
the ELDK toolchain, and I use exactly the same compiler:
$ eldk-switch -r 5.2.1 powerpc
$ which powerpc-linux-gcc
/opt/eldk-5.2.1/powerpc/sysroots/i686-eldk-linux/usr/bin/powerpc-linux/powerpc-linux-gcc

> 
> Actually, running fpu code in kernel space is a bad idea in the
> first place. Xenomai supports this for desperate situations when
> porting relic code absolutely requires it, but this is clearly
> something that should be avoided. You should really consider moving
> all that stuff to userland if the situation is not that desperate.
> 

Yes, I know, that is what we are working on. As I wrote it in my first
letter, we should port our application to Xenomai and run it in userspace.

If it can help here is the test project:
https://gist.github.com/bukulin/4951215
(At the compilation the kernel build directory should be defined with
KSRC=<kernel build directory>)

Thank you four your help, again!

- -- 
Best regards,
Norbert Bukuli
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.19 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

iQEcBAEBAgAGBQJRHJicAAoJEJEs22zQJ00SVDsH/jseNB7qxQiK0ZrcejY0QEJx
GhijebXtI7SxMbDQECYsb6+pEJYdKGtVRNuOQgSdinwe6EM66cUxWUyV4rF++WXu
9jOVlpl5BJF+c0s3S2n+bmmcstNz0Lct0ZE8yhPrDgO4nmk6YjTCYmixplXoeDOx
y3qves9JHSI4tvCMa/P0MDf4XmKRjPviCUadwihx/kwQjt4wxcXj7DOJcacgw/6V
9HSJFKUAk4N7/eV0sNjQWB08hDQJME74cdZ++0lf0llmUh2AQh7AC3LJN4RYR3hO
RGxSezF4n0NhUbEFYdY9U7Rzj26GasRKYTsUQ2Z/OAPGZSkHhIIIBIevb4rMkHI=
=ZtY5
-----END PGP SIGNATURE-----